So we are having a race condition of three of threads, resulting in a
deadlock backoff in purge, which is unexpected.

More precisely, the following happens:
T1: NOCOPY ALTER TABLE begins, and eventually it holds MDL_SHARED_NO_WRITE
 lock;
T2: FLUSH TABLES begins. it sets share->tdc->flushed = true
T3: purge on a record with virtual column begins. it is going to open a
 table. MDL_SHARED_READ lock is acquired therefore.
Since share->tdc->flushed is set, it waits for a TDC purge end.
T1: is going to elevate MDL LOCK to exclusive and therefore has to set
 other waiters to back off.
T3: receives VICTIM status, reports a DEADLOCK, sets OT_BACKOFF_AND_RETRY
 to Open_table_context::m_action

My fix is to allow opening table in purge while flushing. It is already
done the same way in other maintainance facilities like REPAIR TABLE.

Another way would be making an actual backoff, but Open_table_context
does not allow to distinguish it from other failure types, which still
seem to be unexpected. Making this would require hacking into
Open_table_context interface for no benefit, in comparison to passing
MYSQL_OPEN_IGNORE_FLUSH during table open.

innodb_debug_sync was introduced in commit
b393e2cb and reverted in
commit fc58c172 due to memory leak reported
by valgrind, see MDEV-21336.

The leak is now fixed by adding `rw_lock_free(&slot->debug_sync_lock)`
after background thread working loop is finished, and the patch is
reapplied, with respect to c++98 fixes by Marko.

The missing DEBUG_SYNC for MDEV-18546 in row0vers.cc is also reapplied.

Quoting MDEV reporter Daniel Lewart:

Starting MariaDB with default configuration causes the following problems:

    "[Warning] Could not increase number of max_open_files to more than 16384 (request: 32186)"
    silently reduces table_open_cache_instances from 8 (default) to 4

Default Server System Variables:

    extra_max_connections = 1
    max_connections = 151
    table_open_cache = 2000
    table_open_cache_instances = 8
    thread_pool_size = 4

LimitNOFILE=16834 is in the following files:

    support-files/mariadb.service.in
    support-files/mariadb@.service.in

Looking at sql/mysqld.cc lines 3837-3917:
wanted_files= (extra_files + max_connections + extra_max_connections +
tc_size * 2 * tc_instances);
wanted_files+= threadpool_size;

Plugging in the default values:
wanted_files = (30 + 151 + 1 + 2000 * 2 * 8 + 4) = 32186

However, systemd configuration has LimitNOFILE = 16384, which is far smaller.

I suggest increasing LimitNOFILE to 32768.

(trivial backport to 10.2)
Add a testcase

(trivial backport to 10.2)
The optimizer removes redundant GROUP BY operations. If GROUP BY element
is a subselect, it is "eliminated".

However one must not eliminate the item if it is used both in the select
list and in the GROUP BY, like so:

  select (select ... ) as SUBQ from ... group by SUBQ

Do not eliminate such items.

It is possible that an object that was originally created by
open_purge_table() will remain cached and reused for SQL execution.
Our previous fix wrongly assumed that ha_innobase::open() would
always be called before SQL execution starts. Therefore, we must
invoke dict_stats_init() in ha_innobase::info_low() instead of
only doing it in ha_innobase::open().

Note: Concurrent execution of dict_stats_init() on the same table
is possible, but it also was possible between two calls to
ha_innobase::open(), with no ill effects observed.

This should fix the assertion failure on stat_initialized.
A possibly easy way to reproduce it would have been
to run the server with innodb_force_recovery=2 (disable the purge of
history), update a table so that an indexed virtual column will be
affected, and finally restart the server normally (purge enabled),
to observe a crash when the table is accessed from SQL.

The problem was first observed and this fix verified by
Elena Stepanova. Also Thirunarayanan Balathandayuthapani
repeated the problem.

row_sel_sec_rec_is_for_clust_rec(): If the field in the
clustered index record stored off page, always fetch it,
also when the secondary index field has been built on the
entire column. This was broken ever since the InnoDB Plugin
for MySQL Server 5.1 introduced ROW_FORMAT=DYNAMIC and
ROW_FORMAT=COMPRESSED for InnoDB tables. That code was first
introduced in this tree in
commit 3945d5e5.

For the original ROW_FORMAT=REDUNDANT and the MySQL 5.0.3
ROW_FORMAT=COMPRESSED, there was no problem, because for
those tables we always stored at least a 768-byte prefix of
each column in the clustered index record.

row_sel_sec_rec_is_for_blob(): Allow prefix_len==0 for matching
the full column.

Before FRM is written walk vcol expressions through
check_table_name_processor() and check if field items match (db,
table_name) qualifier.

We cannot do this in check_vcol_func_processor() as there is already
no table name qualifiers in expressions of written and loaded FRM.

Buffer overflow in ib_push_warning() fixed by using vsnprintf().

InnoDB parser was obsoleted by MDEV-16417.

Thanks to Nikita Malyavin for review and suggestion.

It's Oracle libmysqlclient license exception, we no longer include,
build or ship libmysqlclient

Before this patch mergeable derived tables / view used in a multi-table
update / delete were merged before the preparation stage.
When the merge of a derived table / view is performed the on expression
attached to it is fixed and ANDed with the where condition of the select S
containing this derived table / view. It happens after the specification of
the derived table / view has been merged into S. If the ON expression refers
to a non existing field an error is reported and some other mergeable derived
tables / views remain unmerged. It's not a problem if the multi-table
update / delete statement is standalone. Yet if it is used in a stored
procedure the select with incompletely merged derived tables / views may
cause a problem for the second call of the procedure. This does not happen
for select queries using derived tables / views, because in this case their
specifications are merged after the preparation stage at which all ON
expressions are fixed.
This patch makes sure that merging of the derived tables / views used in a
multi-table update / delete statement is performed after the preparation
stage.

Approved by Oleksandr Byelkin <sanja@mariadb.com>

Fix is to changed message to be [WARNING] for backup

There is new Yukon Standard time Windows timezone.

Also fix the powershell script that generates the Windows locale mapping,
tell powershell to use TLSv1.2 to access the github (on some reason it is
TLS1.1 that powershell is using by default, and it does no work)

		to mysql interpreter

InnoDB returns uninitialized statistics to mysql interpreter
when background thread is opening the table. So it leads to
assertion failure. In that case, InnoDB avoid sending
innodb statistics information to mysql interpreter.

node->index was NULL.
But it's possible to get dict_table_t* from another source.

There was race between a committing transaction and the following in binlog
order FLUSH LOGS that could create a 2nd Binlog checkpoint (BCP) event
in the new file *before* the first logged-in-old-binlog transaction gets committed in
Innodb. That would cause the transaction loss at recovery, should
the server stop right after the BCP.

The race is tackled by enforcing the necessary set of mutexes to be acquired
by FLUSH-LOGS handler in the correct order (of the group commit leader
pattern).

Note, there remain two cases where a similar race is still possible:
  - the above race as it is when the server is run with ("unlikely")
    non-default `--binlog-optimize-thread-scheduling=0` (MDEV-24530), and
  - at unlikely event of bin-logging of Incident event (MDEV-24531) that
    also triggers binlog rotation,
    in both cases though with lesser chances after the current fixes.

Closes #1811

Since it ended up being a plain text file rather than a script
(post-fix for MDEV-25288)
Also removed main-test_sql_discovery.create from the list,
as a workaround for MDEV-25384. The bug only affects 10.3+,
but it will be simpler if 10.2 part of the tests is the same
in all branches

... to run upon building/packaging of MariaDB server

Eliminate a memory leak when init can fail by forgetting to delete the
Event_queue_element_for_exec object.

PROBLEM
-------

1. The customer had presented a stack which had many threads waiting on
   multiple mutexes like LOCK_Status, srv_innodb_monitor_mutex,  ibuf_mutex etc.
2. The root cause was that the AHI latch was held in S (shared) mode by the a thread which was
   doing a truncate of a large table .
3. There was another thread which was trying to acquire the AHI latch in X (exclusive) mode
4. With our lock implementation any thread requesting a X lock ,blocks rest of the threads
   requesting S(shared) locks,this caused many threads to wait for this shared lock.
5. The main reason why we hold the latches in truncate is to avoid disabling of AHI
   during truncate

FIX

This patch sets the proper name resolution context for outer references
used in a subquery from an ON clause. Usually this context is more narrow
than the name resolution context of the parent select that were used before
this fix.
This fix revealed another problem that concerned ON expressions used in
from clauses of specifications of derived tables / views / CTEs. The name
resolution outer context for such ON expression must be set to NULL to
prevent name resolution beyond the derived table where it is used.
The solution to resolve this problem applied in sql_derived.cc was provided
by Sergei Petrunia <sergey@mariadb.com>.

The change in sql_parse.cc is not good for 10.4+. A corresponding diff for
10.4+ will be provided in JIRA entry for this bug.

Approved by Oleksandr Byelkin <sanja@mariadb.com>

It seems some overly tolerant compilers (gcc) allow the structure
of IO_CACHE that is defined differently in libmaria to have
members equalivance to the iocache in mysys.

More strict Solaris compilers recognise that rc_pos really
isn't a structure member and won't compile.

Make Item_subselect::walk() walk the ON expressions, too.

MDEV-22255 SIGABRT: Assertion `id' failed in trx_write_trx_id on INSERT | Assertion `id > 0' failed in trx_write_trx_id | Assertion `val > 0' failed in row_upd_index_entry_sys_field | Assertion `thr_get_trx(thr)->id || index->table->no_rollback()' failed.

InnoDB purge thread locks the root page of clustered index
while accessing the undo log records and later same thread
tries to open the table, initialize statistics and tries
to lock the clustered index root page while doing virtual
column computation.

Solution:
=========
InnoDB should prevent statistics initialization when the
table is being opened by purge thread

When a column is added to an non-empty table, existing rows will have
a column's default value for existing rows. Or a "zero value" if the
column has no default.

But this check should be skipped when an existing column is altered.

signal handler, display coredump file pattern similarly to MDEV-25294 but for FreeBSD, thankfully the sysctl OID is the same.

also add =WARN as an alias for =OFF
and clarify the help text

- Fixing post-fix failure. In clean_new_vcol_index(), InnoDB has the wrong
offset to store the virtual column

MDEV-24135: Print warnings in XML, save test retries in XML, save the combinations in XML, replace the special symbols in the XML comment

At the second execution of the PS
1. mark_as_dependent() is called with the same parameters as at the first
   execution (select#4 and select#3)
2. as outer_select (select#3) has been already merged at the first
   execution of PS it cannot be reached using the outer_select() function
   anymore (and so can not stop iteration).
3. as a result all selects towards the top level select including the
   select for 'ca' are marked as uncacheable.
4. Marked uncacheable it executed incorrectly triggering filling its
   temporary table several times and using freed memory at the end.

To avoid the problem we use name resolution context to go "up".

NOTE: problem also exists in 10.2 but has no visible effect on execution.
That is why the problem is fixed in 10.2.

The patch also add debug logging of important procedures and
better specify parameters types of st_select_lex::mark_as_dependent.